3-Isothiazolones are known compounds. In their practical use, for example, as bactericidal, fungicidal or algicidal materials, they have the disadvantage that they decompose relatively easily in solution and thereby become ineffective and in some cases also form undesired by-products.
In the past, attempts have been made to improve the stability of 3-isothiazolones by the addition of, for example, solvents, chlorides, nitrates or other salts, formaldehyde, formaldehyde-forming materials as well as orthoesters or other organic compounds. Such methods are described, for example, in U.S. Pat. Nos. 3,870,795 and 4,067,878 (metal nitrates and nitrites); U.S. Pat. Nos. 4,129,448 and 4,165,318 (formaldehyde); and U.S. Pat. No. 4,824,957 (organic hydroxylic solvents). EP-A 147,223 discloses preservative or disinfectant compositions comprising an organic biocide (including isothiazolones) and an organic hydroperoxide (aliphatic or aromatic). This patent does not disclose stabilizing properties of hydroperoxides. In EP-A 0 315 464 stabilized 3-isothiazolone-containing mixtures are described. Orthoesters of formic, acetic, or benzoic acid serve as stabilizers therein. However, this is very costly.
EP-A 0 300 483 discloses 3-isothiazolones which can be stabilized by the addition of relatively complex synthetic organic compounds such as hydroquinones or quinones, alone, or in combination with synergists such as metal nitrates and potassium permanganate.
In many cases of the use of 3-isothiazolones, it is desirable for various reasons to diminish the content of the above-noted known stabilizers in the biocides containing the 3-isothiazolones. For example, it is also known that dispersions or emulsions which require microbiocidal protection are sensitive with respect to the addition of salts. This is true particularly if the salts contain divalent ions. Promoted by poor mixing, coagulates then easily arise, which adversely affect the quality of the dispersion or emulsion.
Furthermore, the microbiocidally active components can become enclosed in these coagulates. Thereby only fractions or in an unfavorable case no microbiocidally-active materials are available. This is especially true if the products to be preserved are filtered.
These undesired actions of the above-noted components in biocides containing isothiazolones also arise in some formulations which have been stabilized with low salt concentrations or salt free hydroxyl group-containing solvents.
Furthermore, there are formulations which should contain none or only a small concentration of chloride since otherwise damaging incompatibilities arise. Additionally, by a diminution of the chloride content, the corrosion action of the formulation is also reduced.
In isothiazolone formulations which are stabilized by nitrates, there is the danger of the introduction or the formation of nitrosamines. The latter are suspected of having carcinogenic properties. Accordingly there is a substantial need to avoid nitrates for stabilization or to reduce their quantity. In the case of formaldehyde and formaldehyde-yielding materials as stabilizers, it has been shown at least in animal experiments that formaldehyde acts carcinogenically.
The object underlying the present invention is to provide a method for the stabilization of aqueous solutions of one or more isothiazolones which makes it possible to reduce or even wholly avoid the content previously necessary for stabilization of chloride, nitrate (and the undesired nitrosamine formation bound up with that), nitrite, other metal salts, formaldehyde, formaldehyde-yielding materials and/or solvents (with the exception of water).